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Thread: Nose Gear Strut Crack

  1. #11
    Senior Member Dave S's Avatar
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    Default Re: Nose Gear Strut Crack

    Skot,

    I'd agree with the folks indicating re-welding by a competent person if the only issue is a crack with no other underlying problems such as corrosion.

    If I understand the photo correctly, this looks to be the bottom of the strut where it is welded to the tube which the nose wheel fork swivels on.....Correct?

    I'd check an additional item ......the vertical tube which the nose wheel fork swings on calls for inserting a foam plug during original assembly/build, sealed with hysol up the inside of the threaded end an inch or so to clear the cotter pin.....the reason for this is to seal the vertical tube from moisture and corrosion. Due to the location down in the weeds - this spot is particularily succeptible to corrosion as the inside is not painted or powdercoated. Checking the integrity of this plug is an annual condition inspection point. If the plug is not there, or is damaged, this is a particularily nasty place for moisture to get up and rot the vertical tube from the inside out. The weld is basically naked and unprotected on the inside of the tube without the plug. Tube rust/corrosion from the inside out can make a weak spot where developement of a crack could be a secondary effect of corrosion/rust/thinning of the metal.

    If the original plug is intact and no rusting - the plug will likely have to be renewed after welding/treatment as it will probably fry from the welding.

    Buying a new one is a certain way to go if it ends up the original can't be safely fixed.


    Sincerely,

    Dave S
    KF 7 Trigear
    912ULS Warp Drive

  2. #12
    Senior Member SkyPirate's Avatar
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    Default Re: Nose Gear Strut Crack

    Being a retired certified welder I would either tig it or flame weld it, and as soon as I got it welded I would flash heat it so it didn't cool fast then wrap it up in some old welding gloves and go to lunch, when I got back I would check it, it should be cool to touch then I would walnut blast the area prime it paint it and re install, if you have to mig weld it preheat the repair area to about 300 degrees, flash heat it with a torch, don't hold it in one spot making it cherry red, just flash the flame evenly across the repair area, weld it wrap it cool it walnut blast it paint it
    Chase
    Model 5 OutBack
    912 UL

  3. #13

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    Default Re: Nose Gear Strut Crack

    Quote Originally Posted by SkyPirate View Post
    Being a retired certified welder I would either tig it or flame weld it, and as soon as I got it welded I would flash heat it so it didn't cool fast then wrap it up in some old welding gloves and go to lunch, when I got back I would check it, it should be cool to touch then I would walnut blast the area prime it paint it and re install, if you have to mig weld it preheat the repair area to about 300 degrees, flash heat it with a torch, don't hold it in one spot making it cherry red, just flash the flame evenly across the repair area, weld it wrap it cool it walnut blast it paint it
    I agree with Chase,
    I might add a gusset made from 4130 tubing cut in half,length-wise, and placed
    45 degrees between the two tubes and over the original crack. This would move the stress point away from the original repaired area.

  4. #14
    SWeidemann's Avatar
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    Default Re: Nose Gear Strut Crack

    In reply to Dave, Chase & Others:

    I did find there is NO foam plug in the bottom (just above the big keyed nut on the pile of Belleville washers), but it doesn't look too bad inside.

    From a certified welder's perspective, the technique for a repair sounds like an orchestrated procedure that should be left to some one who knows what to do.

    As a point of interest, I was told that the nose wheel strut is at least the second one installed on this aircraft in it's lifetime. There was some kind of "event" in it's sketchy past that preciptated the purchase of a new unit from Kitfox, however nothing at all in the log book. I am guessing the spot where I found the crack may be a common weak point?

    I have an email in to Debra & John at Kitfox to get info from them about a repair or replacement. (Message is they are out til Jan 5)

    Thanks guys for all your replies,

    Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  5. #15

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    Default Re: Nose Gear Strut Crack

    One more opinion. It's great that you posted a photo but I can't be sure from the photo exactly what happened there but it may be that there simply was no weld penetration into the piece that appears to have cracked. What we are looking at may just be the edge of the filler wire bead that failed to get the metal hot enough to melt it and make a good weld. Even if there was some penetration, it may not have been deep enough to make a strong enough weld for the application and this may have allowed the filler bead to break away from the part creating what looks like a crack when it may just be a bad weld. If the metal of the strut did fracture I would replace it, but if it is just a bad weld then rewelding it is the appropriate fix. Like others have suggested I would TIG or GAS weld it with my personal preference being TIG.

  6. #16
    SWeidemann's Avatar
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    Default Re: Nose Gear Strut Crack

    Silverfox,

    My intent is to take the strut to my regular IA for a look and also my local EAA Technical Counselor. John & Debra's opinion will count too. My guess is it may be a weld issue of not much significance and may have been there for some time. An option is to paint the spot and keep up regular inspections to see if ther is any new cracking activity. However if my IA doesn't like it I will need a fix. I know a new strut will be $$$.

    Thanks much, Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  7. #17
    Senior Member PapuaPilot's Avatar
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    Default Re: Nose Gear Strut Crack

    Hopefully all of the people you mention will recommend fixing or replacing it. Do you really want to fly your plane with a crack on the landing gear?

    If your nose gear fails and collapses what would the cost be then?
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  8. #18

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    Default Re: Nose Gear Strut Crack

    Quote Originally Posted by SWeidemann View Post
    Silverfox,

    My intent is to take the strut to my regular IA for a look and also my local EAA Technical Counselor. John & Debra's opinion will count too. My guess is it may be a weld issue of not much significance and may have been there for some time. An option is to paint the spot and keep up regular inspections to see if ther is any new cracking activity. However if my IA doesn't like it I will need a fix. I know a new strut will be $$$.

    Thanks much, Skot
    Paint and fly is not an option in my opinion. It is always cheaper to fix it right the first time.
    Kurt A

    Kitfox II,
    Rotax 912,
    1100 gross
    Fixer Upper Project

  9. #19
    SWeidemann's Avatar
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    Default Re: Nose Gear Strut Crack

    Nose Gear Strut Crack Follow Up:

    I showed the cracked unit to a couple of the mechanics at the FBO. They thought a welding repair would be acceptable and recommended a local welding specialty shop.

    Attached is a photo of the finished repair in the form of a stout gusset welded in. I am in the process of re-finishing it in preparation for return to service.

    Thanks for all your comments & suggestions.

    Skot
    Attached Images Attached Images
    Kitfox Vixen 912 ULS
    N24V at C29

  10. #20
    Senior Member Dave S's Avatar
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    Default Re: Nose Gear Strut Crack

    Hey Skot....Looks better than new!

    Having done some welding W/ 4130 steel.......I'd say that you can rest assured a welded repair on a 4130 steel assembly by a competent welder will be solid.

    Regarding the original cause, I tend to cast my opinion with the contributors who indicate it might have been caused by a lack of weld penetration.

    On weld penetration - too much or too little is not good.

    I am including a photo of an example of where too much was an issue.....

    I WANT TO BE SURE EVERYONE UNDERSTANDS THE ASSEMBLY IN THE PHOTO WAS FROM A FUSELAGE WELDMENT MANUFACTURED PRIOR TO WHEN JOHN AND DEBRA HAD THE COMPANY.

    The bracket with the broken tab is where the co-pilot's rudder pedal adjustment is anchored. The very small dark area on the edge of the broken part is all that was holding this half of the tab....all it took was a little push with my thumb...Plink!...it fell off.....the weld process was likely a bit too hot & penetrated into the angle to almost cut the tab off. If you check the other side - you will notice the weld had also eroded a good part of the angle on the other tab also. Didn't take much to fix it using the correct rod & gas torch - and a bit of "normalizing". Needless to say, I did a pretty darn thorough inspection with a hand lense to examine every other weld on the fuse...no other anomolies were found.

    Sincerely,

    Dave S
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